The present technology relates to data storage.
A variety of materials show reversible resistance-change or resistance-switching behavior in which the resistance of the material is a function of the history of the current through, and/or voltage across, the material. These materials include chalcogenides, carbon polymers, perovskites, and certain metal oxides (MeOx) and metal nitrides (MeN). Specifically, there are metal oxides and nitrides which include only one metal and exhibit reliable resistance switching behavior. This group includes, for example, Nickel Oxide (NiO), Niobium Oxide (Nb2O5), Titanium Dioxide (TiO2), Hafnium Oxide (HfO2) Aluminum Oxide (Al2O3), Magnesium Oxide (MgOx), Chromium Dioxide (CrO2), Vanadium Oxide (VO), Boron Nitride (BN), and Aluminum Nitride (AlN).
A resistance-switching element comprising one of these materials may be formed in an initial state, for example, a relatively low-resistance state. Upon application of sufficient voltage, the material switches to a stable high-resistance state which is maintained even after the voltage is removed. This resistance switching is reversible such that subsequent application of an appropriate current or voltage can serve to return the resistance-switching element to a stable low-resistance state which is maintained even after the voltage or current is removed. This conversion can be repeated many times. For some materials, the initial state is high-resistance rather than low-resistance. A set process may refer to switching the material from high to low resistance, while a reset process may refer to switching the material from low to high resistance. A resistance-switching memory cell can include a resistance-switching element positioned between first and second electrodes.
These reversible resistance-change materials are of interest for use in nonvolatile memory arrays. One resistance state may correspond to a data “0,” for example, while the other resistance state corresponds to a data “1.” Some of these materials may have more than two stable resistance states. Moreover, in a resistance-switching memory cell, the resistance-switching element can be in series with a steering element such as a diode or transistor, which selectively limits the voltage across, and/or the current flow through, the resistance-switching element. For example, a diode can allow current to flow in only one direction of the resistance-switching element while essentially preventing a current flow in the opposite direction. Such a steering element itself is not typically a resistance-change material. Instead, the steering element allows a resistance-switching memory cell to be written to, and/or read from, without affecting the state of other memory cells in an array.
However, there is a continuing need for technologies which allow memory cells to be scaled down in size.